Support running on Windows

[gabritto]

We should support running dts-critic on Windows. So far dts-critic v3 was not tested on Windows, and the child_process command execution calls (like execFileSync and spawnSync) don't work. For example, running dts-critic on Windows for webpack gives the following error:

C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic>node dist/index --dts=../DefinitelyTyped/types/webpack/index.d.ts --debug
C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic\dist\index.js:153
    if (info.error !== undefined) {
             ^

TypeError: Cannot read property 'error' of null
    at getNpmInfo (C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic\dist\index.js:153:14)
    at dtsCritic (C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic\dist\index.js:63:21)
    at main (C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic\dist\index.js:138:20)
    at Object.<anonymous> (C:\Users\t-gaar\Desktop\DefinitelyTyped\dts-critic\dist\index.js:832:5)
�[90m    at Module._compile (internal/modules/cjs/loader.js:959:30)�[39m
�[90m    at Object.Module._extensions..js (internal/modules/cjs/loader.js:995:10)�[39m
�[90m    at Module.load (internal/modules/cjs/loader.js:815:32)�[39m
�[90m    at Function.Module._load (internal/modules/cjs/loader.js:727:14)�[39m
�[90m    at Function.Module.runMain (internal/modules/cjs/loader.js:1047:10)�[39m
�[90m    at internal/main/run_main_module.js:17:11�[39m

This happens because this call to spawnSync fails.